Drop-Ins Liners are made to work like mom by gently collapsing. They promote air-free feeding and allow for a more natural breathing and feeding rhythm. Soft, disposable liner contracts while baby feeds to mimic breastfeeding. This prevents air from mixing with milk and allows airfree feeding, reducing colic, gas and fussiness. Pre-sterilized liners guarantee your bottle is clean* and minimize clean-up time. They are also recyclable**. (*Does not include nipple and ring) (**Can be recycled at most grocery and mass retail store recycling bins) Playtex Baby Drop-Ins Liners are specially designed for use with the Playtex Nurser Bottles. Liners are easy to use, disposable and perfect for on the go.